PHASE-TRANSITIONS IN LANGMUIR-BLODGETT-FILMS OF CADMIUM STEARATE - GRAZING-INCIDENCE X-RAY-DIFFRACTION STUDIES

Citation
Jb. Peng et al., PHASE-TRANSITIONS IN LANGMUIR-BLODGETT-FILMS OF CADMIUM STEARATE - GRAZING-INCIDENCE X-RAY-DIFFRACTION STUDIES, Langmuir, 13(6), 1997, pp. 1602-1606
Citations number
20
Categorie Soggetti
Chemistry Physical
Journal title
ISSN journal
07437463
Volume
13
Issue
6
Year of publication
1997
Pages
1602 - 1606
Database
ISI
SICI code
0743-7463(1997)13:6<1602:PILOCS>2.0.ZU;2-O
Abstract
Variations in the structure of multilayer Langmuir-Blodgett (LB) films of cadmium stearate with temperature have been monitored by grazing i ncidence synchrotron X-ray diffraction. At room temperature the film s tructure comprises a centered rectangular unit cell in the plane of th e substrate with the hydrocarbon chains normal to the substrate surfac e. As the temperature increases up to 90 degrees C, the diffraction pa ttern due to this in-plane structure becomes diffuse and the intensity decreases. Changes in the Q-values of the in-plane spots indicate an anisotropic expansion of the unit cell. At around 100 degrees C the fi lm undergoes a phase transition from a layered three-dimensional cryst alline structure to an array of rod structures packed hexagonally. The rods are oriented parallel to the surface of the film. The core of ea ch rod is 6.7 Angstrom in diameter and appears to be composed of cadmi um cations and the carboxylate groups of the fatty acid chains. The al iphatic chains are randomly arranged around these rods. The rod struct ure is retained on cooling, but the observed correlation length is red uced.